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United States Patent |
6,257,516
|
Fritzson
,   et al.
|
July 10, 2001
|
Axial disc brake and yarn feeding device including an axial disc brake
Abstract
An axial disc brake, particularly for a yarn feeding device, having braking
surfaces which are axially pressed against each other with a predetermined
yieldable contact pressure. One of said braking surfaces has a spherical
convex shape, and the other braking surface is conical with a cone axis
lying at least approximately along the axis of the disc brake. The axial
disc brake can be provided at the front end of a storage drum of a yarn
feeding device of a projectile or gripper weaving machine, such that the
yarn withdrawn from the storage drum rotates like the pointer of a clock
along a yarn guiding surface and directly enters into the contact zone of
the braking surfaces without deflection, and is deflected after having
passed the contact zone gently in the axial direction.
Inventors:
|
Fritzson; Joachim (Ulricehamn, SE);
Jacobsson; Kurt Arne Gunnar (Ulricehamn, SE);
Tholander; Lars Helge Gottfrid (Ulricehamn, SE)
|
Assignee:
|
IRO AB (Ulricehamn, SE)
|
Appl. No.:
|
155705 |
Filed:
|
July 26, 1999 |
PCT Filed:
|
March 25, 1997
|
PCT NO:
|
PCT/EP97/01523
|
371 Date:
|
July 26, 1999
|
102(e) Date:
|
July 26, 1999
|
PCT PUB.NO.:
|
WO97/37069 |
PCT PUB. Date:
|
October 9, 1997 |
Foreign Application Priority Data
| Apr 01, 1996[DE] | 196 13 055 |
Current U.S. Class: |
242/365.4; 139/452; 242/150R; 242/419.1 |
Intern'l Class: |
B65H 051/20; B65H 059/22; D03D 047/36 |
Field of Search: |
242/365.4,419.1,150 R
139/452
|
References Cited
U.S. Patent Documents
3455341 | Jul., 1969 | Pfarrwaller et al.
| |
3834635 | Sep., 1974 | Pfarrwaller | 242/365.
|
3897916 | Aug., 1975 | Rosen | 242/365.
|
4017038 | Apr., 1977 | Paepke | 242/365.
|
4059240 | Nov., 1977 | Laursen | 242/365.
|
4153214 | May., 1979 | Savio et al. | 242/365.
|
4161297 | Jul., 1979 | Vella | 242/365.
|
4261526 | Apr., 1981 | Roj | 242/365.
|
4351495 | Sep., 1982 | Lindstrom et al. | 242/365.
|
4799517 | Jan., 1989 | Bucher.
| |
5094275 | Mar., 1992 | Shaw et al. | 139/452.
|
5123455 | Jun., 1992 | Maina | 139/452.
|
5343899 | Sep., 1994 | Jacobsson et al. | 139/452.
|
5409043 | Apr., 1995 | Zenoni et al. | 139/452.
|
5546994 | Aug., 1996 | Sarfati | 139/452.
|
5678779 | Oct., 1997 | Maina | 242/365.
|
6058982 | May., 2000 | Fritzson | 139/452.
|
6095449 | Aug., 2000 | Gallo et al. | 242/365.
|
Foreign Patent Documents |
3640515 | Jun., 1987 | DE.
| |
0 243 565 A1 | Nov., 1987 | EP.
| |
0 536 088 A1 | Apr., 1993 | EP.
| |
0 652 312 A1 | May., 1995 | EP.
| |
855358 | Jul., 1998 | EP.
| |
243 141 | Nov., 1925 | GB.
| |
WO 91/14032 | Sep., 1991 | WO.
| |
9717277 | May., 1997 | WO.
| |
9823520 | Apr., 1998 | WO.
| |
Primary Examiner: Mansen; Michael R.
Attorney, Agent or Firm: Flynn, Thiel, Boutell & Tanis, P.C.
Claims
What is claimed is:
1. A disc brake arrangement comprising a first brake element defining an
axis and a yarn storage area disposed in surrounding relation therewith
from which yarn is withdrawn, and a second brake element supported for
axial movement relative to said first brake element, said first and second
brake elements defining respective brake surfaces which are rotationally
symmetrical about the axis and axially pressed against one another with a
predetermined contact pressure to define a contact zone therebetween, said
braking surfaces together defining a yarn inlet gap adjacent an outer
circumference of said arrangement to permit yarn to enter between said
braking surfaces, one of said braking surfaces having a
spherically-generated convex shape in said contact zone with a radius of
curvature which is centered at the axis of said first brake element, and
the other said braking surface having a conical shape in said contact zone
with a cone axis which substantially coincides with the axis of said first
brake element and a generatrix which forms a tangent to said one braking
surface.
2. The arrangement of claim 1 wherein each of said first and second brake
elements is of a form-stable, substantially rigid construction.
3. The arrangement of claim 1 wherein said one braking surface is defined
on said first brake element and said other braking surface is defined on
said second brake element, said second brake element being disposed
downstream of said first brake element with respect to a direction in
which yarn is withdrawn from said yarn storage area, and the cone axis of
said braking surface of said second brake element intersects the center of
the generating sphere of said braking surface of said first brake element.
4. The arrangement of claim 3 wherein said second brake element has a
frusto-conical shape which defines a centrally-located withdrawal opening
through which yarn withdrawn from said yarn storage area.
5. A yarn feeding device for a textile machine, said yarn feeding device
comprising a yarn storage drum defining an axis and having a front end
which defines a yarn withdrawal region disposed in surrounding relation
with the axis, a disc brake oriented coaxially relative to said storage
drum adjacent said front end thereof, said disc brake including first and
second braking surfaces which are rotationally symmetrical about the axis
and are axially pressed against one other to define a contact zone
therebetween, said first braking surface having a convex shape in said
contact zone with a radius of curvature centered at the axis of said
storage drum, and said second braking surface having a conical shape in
said contact zone with a cone axis which substantially coincides with the
axis of said storage drum and a generatrix which forms a tangent to said
first braking surface in said contact zone.
6. The arrangement of claim 5 further including first and second brake
elements respectively defining said first and second braking surfaces
thereon, said first brake element being disposed at said front end of said
storage drum and said second brake element being disposed downstream of
both said storage drum and said first brake element with respect to a
direction in which yarn is withdrawn from said storage drum, each of said
first and second brake elements having a form-stable, substantially rigid
construction.
7. The arrangement of claim 5 further including first and second brake
elements respectively defining said first and second braking surfaces
thereon, said first brake element being mounted on said front end of said
storage drum and said second brake element being supported for axial
movement relative to said first brake element in a holding device spaced
from said storage drum, said holding device including a drive for
generating a force in at least one axial direction to actuate said second
braking element.
8. The arrangement of claim 7 wherein said first brake element is mounted
at said front end of said storage drum by a fixing element which permits
both limited tilting and limited radial displacement of said first brake
element relative to the axis of said storage drum.
9. The arrangement of claim 8 wherein said first brake element is
constructed of metal or plastic and has a partially spherical shape with
an edge flange which projects away from said second brake element and is
oriented substantially parallel to the axis of said storage drum to
prevent yarn from being caught behind said first brake element, said first
brake element further including a central depression in which said fixing
element is disposed.
10. The arrangement of claim 9 wherein said second brake element has a
frustoconical shape with an outer edge flange oriented transversely
relative to the axis of said storage drum and a centrally oriented
funnel-shaped yarn withdrawal opening having a funnel angle which is less
than a cone angle defined between said second braking surface in said
contact zone and the axis of said storage drum.
11. The arrangement of claim 10 including a membrane fixed to said outer
edge flange of said second brake element which along with said holding
device forms a suction chamber connected to a suction pressure source such
that upon pressurization of said suction chamber, said second brake
element is moved away from said first brake element to allow threading of
a yarn between said first and second braking surfaces.
12. The arrangement of claim 7 wherein said drive includes a spring element
which is disposed to bias said second brake element towards said first
brake element, and an electrically, electromagnetically or pneumatically
actuable return drive connected to said second brake element to apply a
force thereto in opposition to the biasing force of said spring element.
13. The arrangement of claim 7 wherein said drive includes a spring element
which contacts said second brake element in a circle which substantially
corresponds to a circular configuration of said contact zone.
14. The arrangement of claim 5 wherein said yarn withdrawal region defines
a circular yarn-guiding surface and the generatrix of said second braking
surface is approximately tangent to said yarn guiding surface.
15. The arrangement of claim 14 wherein said contact zone is circular and a
diameter thereof is between about 10% and about 50% of a maximum diameter
of said yarn guiding surface.
16. The arrangement of claim 15 wherein the diameter of said contact zone
is about 20% of the maximum diameter of said yarn guiding surface.
17. The arrangement of claim 5 further including first and second brake
elements respectively defining said first and second braking surfaces
thereon, said first brake element being disposed adjacent said front end
of said storage drum and said second brake element being disposed
downstream of said first brake element with respect to a direction in
which yarn is withdrawn from said storage drum, said first and second
brake elements comprising lightweight metal parts and each said first and
second braking surface including a wear-resistant coating thereon.
18. The arrangement of claim 5 wherein said first braking surface is formed
integrally with said storage drum and said second braking surface is
defined on a brake element supported for axial movement relative to said
first braking surface in a holding device spaced from said storage drum,
said holding device including a drive for generating a force in at least
one axial direction to actuate said brake element.
19. The arrangement of claim 5 wherein said storage drum is configured to
store yarn in windings thereon, said arrangement further including first
and second brake elements respectively defining said first and second
braking surfaces thereon, said first brake element being disposed at said
front end of said storage drum and said second brake element being
supported for axial movement relative to said first brake element, said
second brake element being disposed downstream of both said storage drum
and said first brake element with respect to a yarn withdrawal direction
and defining a centrally located yarn withdrawal opening oriented
generally along the axis of said storage drum such that yarn withdrawn
from said storage drum travels between said first and second braking
surfaces and is displaced generally radially into said yarn withdrawal
opening and thereafter travels in a direction substantially parallel to
the axis of said storage drum.
20. The arrangement of claim 19 wherein said contact zone defined between
said first and second braking surfaces has the shape of a circle with a
diameter which remains constant during braking.
Description
FIELD OF THE INVENTION
The present invention relates to an axial disc brake as well as to a yarn
feeding device having an axial disc brake.
BACKGROUND OF THE INVENTION
In an axial disc brake as known from WO91/14032, intended for the weft yarn
rotatingly withdrawn from a storage drum of a yarn feeding device by a
textile machine, in one embodiment the mutually contacting braking
surfaces are provided exactly perpendicular to the axis of the storage
drum. In a further embodiment, the braking surface provided on the front
side of the storage drum is oriented precisely perpendicular to the
storage drum axis, while the other braking surface is formed by a convexly
rounded outer edge of a funnel-shaped braking element having a funnel
angle of almost 180.degree.. The braking surface which is perpendicular to
the storage drum axis in a further embodiment is unitarily formed with the
storage drum. In case of an overhead-withdrawal of the yarn from the
storage drum the yarn is rotating like the pointer of a clock and then is
entering essentially axially and from the outer side in between the
braking surfaces. The yarn is braked by the braking surfaces and then is
withdrawn approximately centrally via an opening provided in one of the
braking surfaces. In the embodiment having braking surfaces oriented
exactly perpendicular to the storage drum axis the yarn is deflected twice
by 90.degree.. Such strong deflection may mean under undesirable
conditions high load for the yarn and might lead to undefined friction
conditions. Centering one of the braking elements on the axis of the
storage drum is without problems because of the orientation of the braking
surface exactly perpendicular to the storage drum axis. However, a lateral
displacement of the braking element, e.g. caused by an axial component of
the yarn tension exerted onto said brake element, may cause a disturbance
of the mutual contact between both braking surfaces. With the strong
deflection of the yarn when entering in between the braking surfaces the
friction force depends on the deflection angle and increases by an
exponential function depending on said deflection angle and might be
superimposed onto the actual braking effect between the braking surfaces.
This might lead to a high yarn breakage quota in case of vulnerable yarn
qualities like cheap woolen- or cotton-yarns of low quality.
In a yarn brake of a yarn feeding device as known from EP-A-652312, a
braking surface having a circumferentially continuous extension and the
shape of a frusto-cone coat directly contacts the rounded withdrawal rim
of the storage drum of said yarn feeding device. The axis of said
frusto-cone coat of said braking surface approximately coincides with the
axis of said storage drum. The other barking surface is defined by said
rounded withdrawal rim of said storage drum and is designed--in an axial
section of said storage drum with a curvature following a circle arc
section. The center of said circle arc section is situated inside said
storage drum, but is positioned a significant radial distance from the
storage drum axis. The frusto-conical braking surface is formed by a
deformable band. In case of precise centering of the band in relation to
the storage drum axis, the contact zone between the braking surfaces is a
full circle. In case that the yarn is forced through the contact zone
and/or a small lateral displacement or tilt of the axis of the frusto-cone
coat occurs in relation to the storage drum axis, the form of the contact
zone changes into a geometrical form other than a full circle.
It is an object of the invention to create an axial disc brake of the kind
as disclosed above as well as a yarn feeding device with which a yarn
geometry can be achieved which is advantageous for the yarn, avoids strong
deflections, and which is accompanied by a correct mutual centering of the
braking surfaces with proper mutual contact relationship in their contact
area between the braking surfaces.
Said task can be achieved according to the invention by providing an axial
disc brake having a pair of form stable braking surfaces axially yieldably
pressed against one another with predetermined contact pressure. The
braking surfaces define an inlet gap in the area of an outer circumference
of the disc brake, with the downstream braking surface having a central
withdrawal opening. A braking element is provided which is movably
supported at least in the axial direction. One of the braking surfaces is
spherically convex with the sphere center thereof located approximately
along the axis of the disc brake, and the other braking surface is conical
with a cone axis approximately coinciding with the axis of the disc brake.
The generatrix of the cone of the other braking surface in the contact
zone of the respective braking surfaces is a tangent to the generating
circle of the spherical other braking surface. The above disc brake can
advantageously be provided on a yarn feeding device for a textile machine,
particularly a projectile or gripper weaving machine, the yarn feeding
device having a yarn storage drum for overhead yarn withdrawal, which
storage drum is provided frontally with a withdrawal region defining a
circular yarn guiding surface, wherein the disc brake is arranged
coaxially with the storage drum adjacent a front end thereof.
Due to the cooperation between the spherical braking surface and the
conical braking surface in contact therewith, the mutual contact zone is
inclined, in which contact zone the withdrawn yarn is braked. The
withdrawn yarn is drawn from the exterior towards the central withdrawal
opening and is simultaneously rotating like the pointer of a clock about
the axis of the disc brake. As a result, a very advantageous yarn geometry
with weak deflection is achieved. The incoming yarn enters into the
contact zone in a straight manner and is then deflected only gently behind
the contact zone and into the withdrawal opening. In addition, constant
contact relationships and a proper mutual centering of the braking
surfaces result from the cooperation of the braking surfaces, since the
contact zone remains a full circle even with deviations of the cone axis
in relation to the axis of the disc brake or the storage drum, and even
when the spherical braking surface becomes displaced. The diameter of said
full circle remains unchangeable due to the geometrical conditions. Due to
the advantageous yarn geometry the danger of yarn breakages is small since
the yarn coming from the yarn guiding surface without deflection enters
the disc brake while rotating like the pointer of a clock and is only
gently deflected behind the contact zone of the braking surfaces. The
reduction of the respective deflection angle and the avoidance of any
deflection in the entrance area of the disc brake has a particularly
positive effect on the yarn, because of the strong exponential influence
of the deflection angle. The yarn is braked practically only in the
contact zone such that the constant braking effect of the braking surfaces
leads to a very advantageous, almost constant yarn tension in the outgoing
yarn. Occasionally occurring relative displacements between the breakage
surfaces do not change the contact- and braking relationships between the
braking surfaces, since the full circle of the contact zone is maintained
constantly as the braking surfaces are apt to automatically mutually align
each other in a correct way. Also manufacturing- or assembling-tolerances
are without significant influence on the braking effect due to the perfect
cooperation between the conical braking surface and the spherical convex
braking surface. The spherical convex braking surface is provided at the
entrance side of the yarn. The center of the sphere is positioned in or
along the axis of the disc brake or the storage drum, respectively.
In one embodiment, the tangent corresponding to the conical braking surface
defines an angle of less than 90.degree. with respect to the brake axis,
and the orientation of the tangent essentially determines the
entrance-direction of the yarn such that the yarn follows an optimal yarn
geometry without deflection at the entrance side and with gentle
deflection at the withdrawal side only.
In another embodiment, a concentric circular yarn guiding surface is
provided upstream of the disc brake and has an outer diameter which is
larger than the outer diameter of the brake. The contact zone between the
braking surfaces is axially spaced from the yarn guiding surface such that
a theoretical extension of the tangent in the contact zone is
approximately tangent to the yarn guiding surface. The disc brake brakes
on a smaller diameter than the diameter of the yarn guiding surface. The
yarn thus follows an optimal path without deflection into the disc brake.
In yet another embodiment, the front side of the storage drum itself
defines the spherical braking surface or supports a braking body having
the spherical braking surface. The other brake element is supported in a
holder and is axially movable. A brake-drive actuates the braking element
with an actuation force which is suitable for the desired braking effect,
and in a yieldable way, such that the braking element is apt to fulfill
all movements necessary during the dynamic phase of the yarn withdrawal
for automatically maintaining a constant braking effect. Space is saved in
the axial direction of the storage drum since the brake elements are
optimally provided close to the storage drum.
In still another embodiment, the braking body is supported at the front end
of the storage drum such that same is capable of tilting to all sides
about a support center, and is additionally supported with radial
clearance. The braking body is apt to automatically adapt to the
respective relative position of the braking element, e.g. by tilting
motions or by radial displacement motions.
The braking body can be made from metal or plastic and has the shape of a
sphere with an outer edge flange and a central depression. The braking
body is thus simple to manufacture and guarantees long periods of time
wherein the brake effect is constant. The edge flange and the centrally
provided depression increase the form staiblity of the brake body and
allow its simple fixation. The edge flange extending rearwardly defines a
safety factor by means of which entrance of the yarn behind the brake body
is prevented in a structually simple way.
The brake element can be made from metal or plastic and has the shape of a
funnel with an outer edge flange and a central yarn funnel having a funnel
angle which is smaller than the cone angle of the conical braking surface.
The brake element is simple to manufacture and guarantees long periods of
time wherein the braking effect is constant. The outer edge flange
increases form stability of the braking element and prevents an accidental
entering of the yarn behind the braking element. The yarn funnel leads to
a gentle withdrawal motion of the yarn and can advantageously serve to
there receive a yarn eyelet for optimum friction- and
deflection-relationships.
A particularly advantageous yarn geometry can be achieved with a cone angle
range of the conical braking surface between 90.degree. and 160.degree..
An optimum value of the cone angle is about 1200 in order to achieve
symmetrical yarn geometry.
To enable an instantaneous and sensitive response of the disc brake, a
diameter range of the circular contact zone of the braking surfaces is
between 10% and 50% of the maximum diameter of the yarn guiding surface.
Having such a relatively small diameter in the contact zone makes it
possible to manufacture the braking elements of lightweight material.
Advantageously, the yarn rotating along the yarn guiding surface like the
pointer of a clock runs freely between the yarn guiding surface and the
contact zone over a relatively long distance such that inherent movements
of the yarn within the distance are not transferred significantly into the
contact zone where they could be detrimental for the braking effect.
Additionally, the long free yarn distance between the yarn guiding surface
and the contact zone results in a strong pointer rotational movement so
that the yarn is drawn in correctly and radially into the contact zone
independent from its linear yarn speed.
In another embodiment, the brake drive is provided with at least one spring
element which contacts the braking element in a circle which is
substantially axially aligned with the contact zone of the braking
surfaces. The contact force between the braking surfaces is precisely
selectable by means of the spring element. The braking element may, if
necessary, yield (also when a knot is passing). It is of particular
importance that the spring element acts approximately in the same diameter
as the diameter of the contact zone such that a straight force
transmission results from the spring element into the contact zone.
In still another embodiment, a membrane is fixed to the edge flange of the
braking element and prevents the entrance of the yarn behind the braking
element. Furthermore, the braking element can be lifted from the braking
body by means of the membrane and a suction actuation of a suction chamber
in order to allow a comfortable threading of the yarn (manually or by
means of a pneumatic threading device). The membrane does not have any
detrimental influence on the normal braking effect. However, the membrane
may contribute to the centering of the braking element.
In a further embodiment, the brake drive is provided with an electrically,
electromagnetically or pneumatically actuatable return drive which
counters the actuation force of the spring element and is connected to the
braking element. Such disc brakes are suitable for projectile or
gripper-weaving machines in order to vary the braking effect during each
insertion cycle depending on the weaving cycle. The return drive
disengages or relieves the axial disc brake in operational phases during
which no or only a minimum braking is necessary, e.g. at the start of an
insertion, after the changeover phase or at the end of the insertion. By
means of the spring elements a basic braking effect is adjusted which then
can be lowered or modulated by the return drive.
The braking element, and also the braking body, may be constructed of
lightweight metal and carry, preferably at the braking surfaces, a
wear-resistant coating.
Since the pointer movement of the yarn entering the disc brake is a basic
prerequisite for an optimum function of the disc brake, it is very
advantageous to combine the axial disc brake with a second upstream
braking device, e.g. a braking device acting in the region of the yarn
guiding surface of the storage drum in order to stabilize the yarn with
low tension in the entrance area into the axial disc brake. The second
braking device may be a braking ring equipped with bristles or the like
cooperating with the storage drum by contact. The geometrical forms of the
spherical or conical braking surfaces need not be exactly derived from a
sphere or a cone. Since the relative displacements of the braking surfaces
have only relatively small magnitudes, an optimally operating axial disc
brake also can be achieved in case both braking surfaces slightly deviate
from a precise geometrical sphere- or cone-shape.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will be explained with reference to the
drawings, in which:
FIG. 1 is a longitudinal section of a first embodiment of an axial disc
brake, and
FIG. 2 is a longitudinal section of a front end-section of a yarn feeding
device having an axial disc brake.
DETAILED DESCRIPTION
An axial disc brake B in FIG. 1 consists in its most important components
of a braking body K against which a coaxial braking element E is pressed
such that braking surfaces 1, 2 which are rotationally symmetrical to the
axis 3 of the disc brake B and which are provided at the braking body K
and at the braking element E are brought against each other with
selectable pre-load in a circle-shaped contact zone C. The axial disc
brake B serves to brake a yarn (not shown) which is drawn through in
between the braking surfaces 1, 2. The phrase "axial disc brake" means
that the drawn through yarn runs parallel to the direction of the axis 3
of the yarn brake and undergoes a displacement into said axis 3. In
operation, the not shown yarn in FIG. 1 enters from the exterior an inlet
gap i formed between the braking body K and braking element E, and then
passes the contact zone C and finally is axially withdrawn through a
centrally provided withdrawal opening e of braking element E.
In FIG. 1 said braking surface 1 is spherical and convex with a sphere
center 4 which coincides with the axis 3 of the disc brake B. The other
braking surface 2 of braking element E cooperating with braking surface 1
is conical and contacts the spherical convex braking surface in the common
contact zone C. The straight generatrix of the conical braking surface 2
thus forms a tangent T at the spherical convex braking surface 1. The cone
angle .alpha. may be between 90.degree. and 160.degree. but is suitably
about 120.degree.. The cone axis 5 of the conical braking surface 2
coincides at least approximately with the axis 3 of the axial disc brake.
Concentric to axis 3 a circular yarn guiding surface 6 is provided at which
the yarn straightly entering into the inlet gap i is guided such that
during its withdrawal motion it carries out a rotating movement like the
pointer of a clock about axis 3 and runs--seen in the direction of axis
3--approximately radially towards axis 3. The diameter of the yarn guiding
surface is bigger than the diameter of the full circle in contact zone C.
The diameter of the full circle in contact zone C may lie e.g. between 10
and 50%, preferably 15 to 25% or about 17%, of the diameter of said yarn
guiding surface 6.
At the braking body K an essentially axial, circumferentially continuous
edge flange 7 can be provided as well as a central depression 8. A fixing
element 9 having a lining 10 engages within depression 8 in order to
support the braking body K at a carrier 10 such that it can be tilted in
limited fashion towards all sides. In addition a radial play 11 is
suitable there in order that the braking body is apt to undergo radial
displacements or movements with limited magnitude. It is possible to load
braking body K with a weak centering spring in FIG. 1 from the left side.
The tilting center 12 of braking body K is preferably situated
approximately in the plane of contact zone C.
Braking element E is of generally funnel-shaped design. An outer radial
edge flange 13 continues the conical braking surface 2. Centrally said
braking surface 2 is provided with said withdrawal opening e which in the
shown embodiment is limited by a funnel section 14 in which a yarn eyelet
15 is located. A cylindrical tube section 16 continues said funnel section
14 and serves as a guiding section. Funnel section 14 is slidably guided
with a small clearance in a guide or sleeve 17. The contact force between
the braking surfaces 1, 2 in contact zone C is generated by a spring
element 18, e.g. a coil spring. The actuation diameter of spring element
18 essentially corresponds to the diameter of the full circle in contact
zone C. In order to indicate the spherical convex braking surface 1 of
braking body K in FIG. 1 more clearly, the contour of braking surface 1 is
extended by dash and dotted lines.
The braking surface respectively supported at carrier 10 could be formed as
a unitary structure with carrier 10. Braking element E as well as braking
body K suitably are metal- or plastic-form parts of a form stable design.
Of particular advantage is to form braking body K and braking element E
from light metal and to provide at least on braking surfaces 1, 2 a wear
resistant coating.
In FIG. 2 the axial disc brake B (e.g. according to FIG. 1) is structurally
integrated into a yarn feeding device F as a so-called weft yarn-output
brake. Only a front end section of a storage drum D of said yarn feeding
device F is shown together with a housing bracket 20. The yarn feeding
device F furthermore is equipped with a housing (not shown) receiving a
drive motor for a winding element, a drive shaft for said winding element
and a bearing for said storage drum B on which a weft yarn Y for a not
shown textile machine, particularly a projectile- or gripper weaving
machine, is intermediately stored for later consumption by the weaving
machine. Said textile machine draws yarn Y overhead of storage drum D and
further in the axial direction (the axis 3 of the axial disc brake B
coincides with the axis of storage drum D). The yarn path is indicated in
dash dotted lines. A conical nose part of storage drum D forms the carrier
10 for braking body K. At the front end of storage drum D a rounded or
conical withdrawal region 19 is provided defining the yarn guiding surface
6 described in connection with FIGS. 1 and 2. During its withdrawal the
yarn Y is running over the yarn guiding surface 6 and is rotating like the
pointer of a clock in the circumferential direction, before in the
direction of the tangent T corresponding to the generatrix of the conical
braking surface in the contact zone C of both braking surfaces it enters
from the exterior between the braking body K and the braking element E.
The yarn is then braked by means of the contact force between both braking
surfaces in contact zone C. Subsequently the yarn is deflected into the
axial withdrawal direction. In the region of yarn guiding surface 6, yarn
Y is deflected inwardly by an angle .alpha./2 from the axial direction,
i.e. half of the cone angle of the conical braking surface, before it runs
in a straight manner into the axial disc brake B. After having passed the
contact zone, the yarn Y is again deflected by the angle .alpha./2 into
the axial withdrawal direction. Advantageously, the cone angle a of the
conical braking surface is adapted to the outer diameter of the yarn
guiding surface 6 and the axial distance between the yarn guiding surface
6 and the deflection area into the axial disc brake such that the
deflections of the yarn at the yarn guiding surface 6 and inside the axial
disc brake are approximately the same.
The longitudinal guide or sleeve 17 of braking element E is part of a
holding device 21 connected to housing bracket 20. In holding device 21 a
brake drive A is provided. In the simplest embodiment spring element 18
serves as brake drive A. Said.spring element 18 is pressing braking
element E against braking body K with predetermined axial actuation force
which e.g. can be adjusted by means of an adjustment screw 25. An
adjustment is carried out by rotating the adjustment screw 25 and
adjusting a stop 24 for spring element 18 in the axial direction inside
holding device 21. In an alternative embodiment (indicated in dotted
lines), a controllable return drive 30 is provided inside holding device
21 which acts upon braking element E counter to the actuation direction of
spring element 18, in order to reduce or modulate the braking effect. Said
return drive 30 can be actuated depending on the weaving cycles, and e.g.
in an electric, electromagnetic or pneumatic manner.
In FIG. 2 the outer edge flange 13 of braking element E is fixed in an
annular membrane 26, the outer edge of which is secured at holding device
21 such that membrane 26 defines a boundary of a suction chamber 27 in
holding device 21. By connecting suction chamber 27 with a suction
pressure source, braking element E can be moved in FIG. 2 to the right
side and can be separated completely from braking body K, e.g. in order to
allow the threading of a new yarn Y. Inside of holding device 21 in the
shown embodiment an ejector-suction- and blowing nozzle 28 is provided by
means of which a suction draft can be generated which is active even in
between the braking surfaces, and simultaneously a blowing flow directed
towards the right side is generated in order to suck in a yarn and to blow
it to the right side, which yarn is brought beforehand into the area of
the then separated braking surfaces. The suction draft also can directly
be used to actuate membrane 26 when it is transferred into suction chamber
27 after actuating ejector nozzle 28. Membrane 26 or return drive 30
generates a forced movement in the direction of an arrow 29 for braking
element E.
The rotating pointer movement of the yarn along the yarn guiding surface 6
and into the axial disc brake B is of particular importance for a proper
function of the axial disc brake. Since consumption of the yarn Y, e.g. by
a weaving machine, takes place intermittently such that during consumption
the yarn speed varies, preferably a second yarn braking device 22 is
provided upstream of the axial disc brake. Said second yarn braking device
22 is supported in a holder 23 at bracket 20 and cooperates with the
withdrawal region 19 of the storage drum. Said second yarn braking device
in the shown embodiment is provided with a rubber membrane and a
frusto-cone-coat-braking band. It is also possible to use a generally
known straw ring or a so-called lamella-brake or a finite band laid flatly
onto the storage drum circumference yieldably tensioned by a tensioning
device. Said second yarn braking device 22 generates only a low basic
tension in the yarn in order to ensure that the yarn Y leaving the
windings on the storage drum D towards inlet gap i of the axial disc brake
cannot come loose and is running properly, and that a balloon formation is
limited or suppressed in this region.
Although a particular preferred embodiment of the invention has been
disclosed in detail for illustrative purposes, it will be recognized that
variations or modifications of the disclosed apparatus, including the
rearrangement of parts, lie within the scope of the present invention.
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